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Old 15-06-2015, 16:10   #16
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Re: Davits

Hmmm... I lean toward high. You could always rig a way to secure the dingy low in "normal" conditions if you ever wanted to it seems. Raise it up for that "perfect storm".
I'm with markJ on not having the dink on the foredeck. If it becomes life or death situation on the davits, "cut 'er free"
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Old 15-06-2015, 16:46   #17
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Re: Davits

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Originally Posted by colemj View Post
Don't tell that to all the sportfishing boats. They would probably invert if they had to make their structures out of steel.

If aluminum is used, it will be sized correctly for the application, so the whole load argument simply goes away. If the davit design is one that is in compression (arch), there won't be much worry about strength. If the design is one where they just stick straight out the back, then steel is the better material, unless they are cast aluminum.

Even when sized correctly, aluminum will be usually be lighter than steel. For simple davits, this may not amount to much difference, but if the structure is going to be larger, like an arch and bimini, it can make quite a difference.

Aesthetically, it is user-choice as to which looks better.

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As I said, each material for its appropriate application. And tuna towers are likewise not analogous to davits. They are welded A frame style structures with multiple diagonals and hard welded joins between the opposing sides, over a wide base footprint. Not so davits. Further, while build thickness etc is determinative of strength for any application, I have regularly seen marine grade aluminium fittings of greater than 5mm thickness corrode to dust in critical areas within half a decade. I have almost never seen an adequately built stainless structure do the equivalent. They can and do fail due to the likes of crevice corrosion, but total failure due to the latter is comparatively rare. Of course aluminium has its place, and is superior to steel in certain applications, particularly those where its comparative strength to weight advantage is critical, such as towers and masts. I am sure it would be adequate for davits as well. However my stainless davits are as new after a quarter century, as have been many other such I have known. Less likely that same number or proportion of aluminium, I would wager.
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Old 15-06-2015, 17:35   #18
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Re: Davits

I think the man was interested in height, as well as material.

Height is a big question. Higher is worse for boat stability, further to hoist, more windage. Lower is asking for the dinghy to get ripped off by breaking wave. It's a very important question and OP should probably get some professional advice. It would be a big mistake to just eyeball it, according to what views he wants.
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Old 15-06-2015, 17:45   #19
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Re: Davits

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I think the man was interested in height, as well as material.

Height is a big question. Higher is worse for boat stability, further to hoist, more windage. Lower is asking for the dinghy to get ripped off by breaking wave. It's a very important question and OP should probably get some professional advice. It would be a big mistake to just eyeball it, according to what views he wants.
Agree. Part of why I dealt so cursorily with that aspect.
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Old 15-06-2015, 19:11   #20
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Re: Davits

High just adds to negative stability. I have never seen a wave break over my swim platform ever. If there was a chance you might be sailing in conditions that it could you should not have a dink on the davits.


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Old 15-06-2015, 20:42   #21
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Re: Davits

Trying to get back to your question, I have a friend who put a low set of davits on his boat. He ran into a problem when the boat heeled over, sometimes the dinghy would hit the water.
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Old 16-06-2015, 02:17   #22
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Re: Davits

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High just adds to negative stability. I have never seen a wave break over my swim platform ever. If there was a chance you might be sailing in conditions that it could you should not have a dink on the davits.


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I can assure you this experience is not universal. And… how do you have a perfect crystal ball for what conditions may be encountered?
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Old 16-06-2015, 05:52   #23
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Re: Davits

The OP did state that he planned to put the dinghy on the foredeck when offshore.

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Old 16-06-2015, 07:47   #24
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Re: Davits

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Originally Posted by colemj View Post
The OP did state that he planned to put the dinghy on the foredeck when offshore.

Mark
Yes, but human nature dictates that when the offshore passage looks like nice whether, he will really wonder whether it's worth the intense bother to do it. Then we know what happens after that . . . better to design the davits to be used in any weather.

I hate my davits and dream about a boat without them, but I will say that they are strong enough, and high enough, to withstand even F9 conditions, and even a knockdown, with a 3.4 meter RIB with 25 hp engine mounted on it, without damage. Tested in real life, unfortunately, last month.
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Old 16-06-2015, 08:35   #25
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Re: Davits

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Originally Posted by Muckle Flugga View Post
I can assure you this experience is not universal. And… how do you have a perfect crystal ball for what conditions may be encountered?

Not all boats are equal, not all engines or sailors are equal.
My boat has a very beamy stern with a walk through transom. Dingy is 10'6" with a four horsepower four stroke outbound. Davits where engineered with a four to one safety factor. Full hoist on dingy brings it forward I foot tight to davits and 6" below stern rail. Dingle is at great heigh to cross and forward tie it so it will not move in a sea way. Totally open rear view minimal negative moment. Bottom of dingy is about 3'6" above the water,outboard is vertical and facing forward.

I would never leave port like this in a uncertain weather forecast, never on a trip greater than seventy miles. I have experience 20+ knots and have got the end of the outboard wet. I have a RF main and reef to keep boat at hull speed with a normal 15-20 degrees of heel, out board does not get wet until 45 degrees.

This works very well for me, on my boat, and on the seas I sail.


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Old 01-07-2015, 19:06   #26
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Re: Davits

First off if he wants favors I say go for it second Sorry to take this on a tangent but at what size vessel do favors make sense space and cost wise?


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Old 02-07-2015, 14:14   #27
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Re: Davits

Sorry meant davits stupid autocorrect


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